This invention relates to switching regulators having the regulator switch commutated into nonconduction for energizing television horizontal deflection circuits while maintaining the horizontal deflection circuit isolated from the power line.
Horizontal deflection circuits are used in conjunction with television picture tubes in television display devices. Typically, the horizontal deflection circuit includes a magnetic winding associated with the picture tube and a switching circuit by which energy from a direct voltage source is coupled to the winding and to its associated reactances. The switching circuit is synchronized with synchronizing signals associated with the information content of the video to be displayed on the picture tube. In order to avoid distorted images on the displayed raster, the size of the horizontal scanning line and the peak deflection or scanning current must be maintained constant over substantial periods of time.
Many conditions can cause the size of the horizontal scanning line to vary. If the direct energizing voltage for the horizontal deflection circuit varies, the scanning energy and hence the width of the horizontal scanning line may vary. It has in the past been customary to regulate the direct voltage applied to the horizontal deflection circuit by the use of a dissipative regulator. Requirements for low power consumption in television receivers are reducing the use of such dissipative regulators in favor of nondissipative or switching types.
Among the switching regulators for use with television deflection circuits are reverse-current regulators, so called because energy in excess of the maximum required by the deflection circuit flows from the regulator to the deflection circuit during a portion of the deflection interval. Regulation is accomplished by variable control of the energy flowing back to the unregulated direct-current source. Such a regulator is described in U.S. Pat. No. 4,013,923 issued Mar. 22, 1977 to den Hollander. When used with an SCR deflection system as illustrated in the den Hollander patent, regulation occurs during the interval in which the commutating switch is open or nonconductive. This interval has a duration of approximately 38 .mu.sec., representing more than half of the 63 .mu.sec. horizontal deflection interval. The reverse-current regulation scheme cannot be conveniently adapted for use with transistor horizontal deflection systems, because only the relatively short retrace interval is available for the regulating action to take place, and also because gating of the return-current switch changes the impedance of the source and adversely affects retrace time.
Forward-current regulators as illustrated by U.S. Pat. No. 4,002,965 issued Jan. 11, 1977 to den Hollander can provide conductive isolation when used in conjunction with a transistor deflection circuit. However, such arrangements require either high-voltage regulator switches or diodes to prevent the application of excessive reverse voltage to the regulator switch during the retrace interval. Also, the gating time variation required to maintain a constant output voltage under conditions of line and load variation is relatively great, thereby limiting the correction range.
A forward-current regulator having a bidirectional regulator switch as described in U.S. Pat. No. 4,071,810 issued Jan. 31, 1978 to Dobbert when used in conjunction with an SCR deflection circuit provides galvanic or conductive isolation between the power source and the deflection circuit and has limited reverse voltage across the regulator switch, but requires a separate controlled resonant circuit to allow the regulator switch to become nonconductive.
It is desirable to have a regulator scheme adaptable for use with a transistor deflection circuit which provides conductive isolation from the power mains, has no substantial voltage across the regulator switch during the retrace interval, a wide range of regulation, and which is commutated off and therefore has relatively small losses and which requires no independent turn-off circuit, or in which turn-off transients are small if a turn-off circuit is used.